In the past, particulate food matter which is suitable for roasting, for example coffee beans, has traditionally been placed within a rotating drum which is heated and/or has hot air blown through it. The process usually takes 5-30 minutes. For approximately two-thirds of this period the charge heats up uniformly and most of the moisture is lost. During the last five minutes or less the temperature of the coffee causes a rapid change of colour. Drum roasting of beans has several disadvantages including slowness, the buffeting of the beans against the sides of the drum or drum baffles with consequent risk of damage to beans and loss of aroma, and the fact that any machine incorporating rotating parts is susceptible to wear and breakdown. In addition, husks detach and burn within the drum causing flavour change.
On a larger scale, coffee beans have been roasted in a fluidized bed roaster in which hot air is admitted to a fluidizing chamber The air enters the fluidizing chamber in a vertical direction and fluidizes a bed of beans within the chamber. The beans remain suspended in hot air in the chamber or may be circulated in a vortex in the chamber until fully roasted. A substantial vertical air flow is required to maintain the fluidized bed in suspension and the whole of the fluidizing air has to be heated to a roasting temperature (typically 250.degree. C. to 300.degree. C.) which results in energy wastage or expensive heat recovery apparatus. Moreover it is difficult to establish and maintain a fluidized bed and the flow conditions required are critical and vary with bean blend and size. Furthermore, bean density varies during roasting as beans lose moisture and swell and air loses its potency as it heats up. These factors further complicate control of a fluidized bed. Fluidized bed roasters have been used for production rates of upwards of 5 Kgs. per hour and while mechanically simpler and quicker than drum roasters are more costly to manufacture and more difficult and costly to operate.
It is an object of the present invention to provide a roaster which ameliorates at least some the disadvantages of prior art. An object of preferred embodiments of the present invention is to provide a roaster which is mechanically simple, and is of less complicated construction and operation than a fluidized bed roaster. A further object of preferred embodiments of the invention is to provide a roaster suitable for use at a point of sale of roasted beans. Such a roaster would be capable of roasting quantities as small as half to one kilogram and be capable of operation by an unskilled operator.